This invention relates, in general, to electronic apparatus and, more specifically, to phasing modules for use with active phased-array antennas.
Active phased-array radar systems have a multitude of signal amplifying and phase shifting modules located at the antenna element positions. These modules amplify the transmitted signals which are then radiated by the antenna elements and also amplify the returned echo signals received by the antenna elements. The modules also furnish the signal phase shifts necessary for obtaining the desired pattern and gain from the antenna system. A manifold system is used to connect all of the modules to the common components of the radar system, such as the pulse signal generator and the echo signal processor.
Traditionally, these modules, which must amplify and phase shift both the transmitted and received signals, have used the same phase shifting components for both the transmitted and the received signals. In order to accomplish this, transmit-receive (T/R) switches were used in the module to switch the phase shifting components, or devices, into either the transmitted signal path or into the received signal path. Certain problems are inherent in switching the phase shifting devices between the transmit and receive paths in the module. These problems include the fact that the phase shifter must work bidirectionally, and also the fact that the phase shifter must handle a comparatively wide range of signal powers. In addition, the phase shifter must operate at different duty cycles in the transmit and receive paths. These requirements limit the types of phase shifter circuits which can be used and require a compromise in the phase shifter design and operating parameters in order to be compatible and functional as the plane shifting component for both the transmitted and received signals.
In addition to the problems associated with a common phase shifter used in the module, several unique characteristics are desirable for the phase shifters in the transmit and receive paths which cannot be easily realized with bidirectional phase shifters. For example, it is often desirable to have a different amount of bit resolution for a digitally controlled phase shifter when working with the transmit or receive signal. Ordinarily, a higher bit resolution is required when shifting phases of the received signal. Also, it is desirable to increase amplification of the amplifiers in the modules without having oscillation problems. It is also desirable to have the ability to compensate for shifter performance with changes in the temperature and frequency of the signal circuit in which they are operating.
Therefore, it is desirable, and it is an object of this invention, to provide a module which removes many of the previous restrictions on phase shifters and affords the realization of the desired characteristics. It is also an object of this invention to provide this type of module in a small, economical and efficient device.